The conventional approach for obtaining accurate quantitative measurements of analyte concentration requires the use of equipment intensive analysis. This approach for determining the concentration of an analyte in a solution requires the use of expensive equipment using spectroscopy, chromatography, NMR, atomic absorption or other analytical procedures that can also be difficult and time consuming to use. Also, a relatively large volume of the solution may be required for the tests.
The use of paper-based microfluidic systems for use in a variety of applications including chemical analysis was first proposed in Martinez, A. W.; Phillips, S. T.; Butte, M.; Whitesides, G. M., Patterned Paper as a Platform for Inexpensive, Low-volume, Portable Bioassays, Angew. Chem. Int. Ed., 2007, 46, 1318-1320. The advantages of using such systems are their low cost and portability. Furthermore, the sample volume amount can be significantly reduced which is helpful when the obtained sample amount is limited (example a biological sample from a hospital patient). It should be noted that the term “paper” is used in the application to refer to cellulosic material including woven fabrics and non-woven material in addition to paper.
Further developments of such paper-based microfluidic systems are described in the applicant's Australian provisional patent application nos. 2008903553 and 2008905776. In the applicant's microfluidic systems, a hydrophobic/hydrophilic contrast is provided on the surface of the paper substrate to thereby define microfluidic channels for controlling the transport of aqueous solutions due to capillary action without the need of external pumping.
The concentration of a test sample may be determined by using colourmetric methods with such microfluidic systems by reacting the test sample with an indicator solution. The accuracy of the results are however influenced by many external factors including environmental conditions such as the ambient temperature and relative humidity, the quality and age of the paper, the quality and the settings of the scanner or camera used to record the results, or the means to transmit the results electronically. This can lead to significant errors in the colorimetric analytical results. Therefore, the same test sample measured using different paper substrates, using different scanners or cameras, or transmitted using different electronic transmission systems with different software could result in significant variations in the result.
The same principle can be used with ELISA-type of analysis based on paper, where bioconjugates are fixed on paper.